With this new process (assuming I have it right), am I right that there's no way to determine whether a file contains overprinting now? No hint in the title bar, no message, no colorization of OP areas?
For that matter, does returning to the Preferences>Page Display to set OP Preview to Never actually turn off the preview in real time? Seems to me I'd have to quit and re-open the application for that change of setting to take effect, no?
You are correct, Overprint Preview > Automatic automatically detects if there is content in the document that requires overprint preview to display it accurately. Changes to the preference should be immediately visible, without having to quit and relaunch. Are you getting different behavior? If so, what OS are you on?
There is one other way to toggle off overprint preview temporarily when it is enabled by the preferences. WIth the Output Preview dialog open, there is a checkbox to turn on/off Simulate Overprinting. This on/off toggling only works while the Output Preview dialog is open.
Color Warnings view in Output Preview should still highlight the objects that are set to overprint. Additionally, you can use Preflight to determine if there is overprinting content in the file. There currently is no message bar or overprint indicator icon.
Also note that, even with the Never setting selected, overprint preview is automatically enabled when the Output Preview dialog is open.
There are a few resources, but unfortunately I don't think all of this information is currently in one place. Help documentation, Leonard's blog, eSeminars, printing guides and, of course, the forums are all useful places to look for info.
I just checked and there isn't an updated printing guide posted yet for Acrobat 9, but there is an Acrobat 8 section in the CS3 guide http://www.adobe.com/designcenter/cs3/articles/cs3_printguide.html
I'd keep an eye out for the CS4 guide which will probably include Acrobat 9 and perhaps more info on the new features/enhancements.